A standard Phase 2 NVC survey was undertaken at Gweunydd Nant y Twyn as part of the Site of Special Scientific Interest (SSSI) designation process.
Gweunydd Nant y Twyn consists of a cluster of small fields, with tall, wooded hedgerows. The site is of particular importance for bryophytes.
The site comprises the original Phase 2 site survey site of Mockridge et al. 1998, which has now been resurveyed (2024) and extended to include several contiguous small fields, and a further extension centred on 5 small nearby fields, approximately 1/3rd of a km to the north, linked by a block of woodland and pasture. The total area of the Phase 2 survey site is now 39.9ha.
